title: The enzyme-mediated direct reversal of a dithymine photoproduct in germinating endospores.
abstract: Spore photoproduct lyase (SPL) repairs a special thymine dimer, 5-thyminyl-5,6-dihydrothymine, which is commonly called spore photoproduct, or SP, in germinating endospores. SP is the exclusive DNA photo-damaging product found in endospores; its generation and swift repair by SPL are responsible for the spores' extremely high UV resistance. Early in vivo studies suggested that SPL utilizes a direct reversal strategy to repair SP in the absence of light. Recently, it has been established that SPL belongs to the radical S-adenosylmethionine (SAM) superfamily. The enzymes in this superfamily utilize a tri-cysteine CXXXCXXC motif to bind a [4Fe-4S] cluster. The cluster provides an electron to the S-adenosylmethionine (SAM) to reductively cleave its C5'-S bond, generating a reactive 5'-deoxyadenosyl (5'-dA) radical. This 5'-dA radical abstracts the proR hydrogen atom from the C6 carbon of SP to initiate the repair process; the resulting SP radical subsequently fragments to generate a putative thymine methyl radical, which accepts a back-donated H atom to yield the repaired TpT. The H atom donor is suggested to be a conserved cysteine141 in B. subtilis SPL; the resulting thiyl radical likely interacts with a neighboring tyrosine99 before oxidizing the 5'-dA to 5'-dA radical and, subsequently, regenerating SAM. These findings suggest SPL to be the first enzyme in the large radical SAM superfamily (>44,000 members) to utilize a radical transfer pathway for catalysis; its study should shed light on the mechanistic understanding of the SAM regeneration process in other members of the superfamily.
authors.affiliation: Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis (IUPUI), 402 N Blackford Street, Indianapolis, IN 46202, USA. lilei@iupui.edu.
authors.forename: Linlin
authors.initials: L
authors.lastname: Yang
authors.forename: Lei
authors.initials: L
authors.lastname: Li
mesh_terms: D002384:Catalysis; D003545:Cysteine / Q000235:genetics; D004247:DNA / Q000378:metabolism; D004260:DNA Repair; D012436:S-Adenosylmethionine / Q000737:chemistry
chemical_list: D012436:S-Adenosylmethionine; D004247:DNA; D003545:Cysteine